LBR was a container format popular for distributing CP/M software, designed by Gary P. Novosielski. Since it had no compression of its own, it was common for individual members of .LBR files to be compressed with Squeeze (.?Q?), Crunch (.?Z?), or CrLZH (.?Y?). Alternatively, the whole library could be compressed with one of these methods (leading to the extensions .LQR, .LZR, .LYR).

Under CP/M, the canonical tools for manipulating LBR files were LU.COM and NULU.COM. Other tools, such as NSWP.COM, understood both LBR and some of the closely associated compression formats.